Historians of the future, themselves as yet barely out of disposable nappies, may look back on March 2007 and decide that this latest unseasonably mild month marked a pivotal moment in British history. It was the month, Professor Peter Hennessy's successor of 2057 may conclude, when the politics of climate change, which had rumbled ineffectually in the margins of British political life for at least 20 years, finally began to get serious.

Three striking pieces of evidence helped this future Hennessy to buttress his claim. The first was the European Union's decision in March 2007 to set tough and popular targets on renewable energy use and the reduction of carbon dioxide emissions. Before that EU decision, the historian observed, most people in this country still lit their houses with wasteful filament light bulbs. It was not uncommon, even as late as 2007, for whole office buildings in British cities to remain lit up all night without the slightest penalty. By 2020, however, all this had changed dramatically. No switched-on company could remain commercially viable in the face of EU laws and, more important, of consumer revolts coordinated by the online anti-waste movement. In the home, the filament bulb soon became a museum piece, as the coal fire had done 50 years previously. Though politicians of this period were slow to spot it, this also marked the moment when the EU began to establish itself as an effective and later even as a popular institution.

The second crucial change was the publication, only a week after the Brussels EU summit, of Britain's first significant climate change legislation. It may seem hard to believe it now, looking back from 2057 and knowing what we do, but in 2007 the future Labour leader Gordon Brown fought to stop the bill introduced by environment secretary David Miliband - later Brown's successor - from earmarking carbon taxes for the environmental transformation of British life that successive governments were to carry out over decades. At the time the bill was criticised for its caution.

Such criticism partly lay behind the third big change of that astonishing month. When he became Conservative leader in 2005, few predicted how quickly David Cameron would capture the green agenda for the Tory party. But Cameron's audacious announcement that his party intended to increase the environmental taxes on air travel marked the moment when many sceptics finally set their doubts aside. Labour criticised the announcement as headline grabbing - but it was a headline that captured the public mood. The rest, as we now know, is history. If only political life today was as inspiring as political life in March 2007.